Whole crudes and crude fractions with high petroleum acid and calcium content are corrosive to the equipment used to extract, transport and process the crude. Additionally, calcium deposition on equipment used to process such crudes damages such equipment and interferes with subsequent processing steps.
Efforts to minimize naphthenic acid corrosion and calcium content in crudes and crude fractions have included a number of approaches. U.S. Pat. No. 5,182,013 refers to such recognized approaches as blending of higher naphthenic acid content oil with low naphthenic acid content oil. Additionally, a variety of attempts have been made to address the problem by using corrosion inhibitors for the metal surfaces of equipment exposed to the acids, or by neutralizing and removing the acids from the oil. For example, Kalichevsky and Kobe in Petroleum Refining with Chemicals (1956), Chapter 4 discloses various alkali treatments of crudes and crude fractions. U.S. Pat. No. 4,199,440 which teaches the use of difficult-to-break caustic-in-oil emulsions discloses treatment of a liquid hydrocarbon with a dilute aqueous alkaline solution, specifically dilute aqueous NaOH or KOH in conjunction with a filtration/coalescing bed. Dilute aqueous base was required in order to effect solubility of the naphthenic acids in the aqueous phase without encountering emulsion formation, which was disclosed to be undesirable. U.S. Pat. No. 4,300,995 discloses the treatment of carbonous material particularly coal and its products, heavy oils, vacuum gas oil, petroleum resids having acidic functionalities with a dilute quaternary base such as tetramethylammonium hydroxide in a liquid (alcohol or water) at a temperature of 100.degree. C. to 300.degree. C. IR data of the untreated crude show a peak at 3300-3600 cm.sup.-1 corresponding to a phenolic hydroxide (Example 6). The C.sup.13 NMR spectrum of o-methylated crude shows a signal at 55 ppm corresponding to a methyl phenoxide (Examples 3 and 4). This patent was aimed at improving yields and physical characteristics of the products by producing alkylated products of inter alia acidic functionalities and did not address the question of calcium reduction or neutralization of acidic functionalities. Kalichevsky and Kobe as well as U.S. Pat. No. 4,199,440 note, however, that a problem arises because certain aqueous base solutions form stable caustic-in-oil emulsions, necessitating use of only dilute aqueous base solutions. Additionally, these references typically treat crudes and crude fractions that previously have been acid pretreated (e.g., with H.sub.2 SO.sub.4).
While these processes have achieved varying degrees of success, they do not address the dual treatment of acidic calcium containing crudes. Thus, there is a continuing need to develop more efficient methods for treating such calcium containing crudes.